But with two preseason games remaining, Acker is playing well and could still be in position to make an impact as a rookie, both on special teams and as a reserve cornerback.

Against the Broncos Sunday in Denver’s 34-0 victory over San Francisco, Acker had several standout plays, capping a successful week in which he also had two interceptions in practice.

Acker had a slow start to camp, trying to catch up and make the right reads, but now the former SMU standout is playing with much more confidence.

“My first couple of weeks were a learning experience,” he told Matt Barrows of the Sacramento Bee. “Now it’s time to play.”

Acker played 25 snaps against Denver and broke up a pass, drew offensive pass interference and made an interception that was wiped out by a penalty. Eric Branch of the San Francisco Chronicle also reported that Pro Football Focus determined Acker allowed just one catch on two targets for 5 yards, while fellow rookie Johnson allowed three catches on three targets for 53 yards.

Acker told Kevin Lynch of the Chronicle that he’s learned a lot from his coaches and veteran teammates this summer, including how to use his outside hand – the one away from the receiver – to knock away passes, because officials are less likely to call pass interference.

At this point, Acker knows if he can continue to make progress, he has a chance to make the opening-game roster on Sept. 7 vs. Dallas. He’ll get his next opportunity to show what he can do this Sunday against the Chargers at Levi’s Stadium.

“The coaches sat us all down after the first game and really talked to us how everyone has a chance to be on the team and there’s an opportunity for us to make a play on any play,” he told the Sacramento Bee.

Derrick Odum, who was Acker’s secondary coach at SMU, believes Acker is a terrific athlete who can blossom into a good NFL player with experience. Odum told a writer for the 49ers website that because Acker was an all-purpose player for his high school team, he never mastered techniques and fundamentals until late in his college career.

By his senior year, he started to flourish.

“He understood how important technique was to his position,” Odum said. “It gave him an advantage right away. He really worked on the little nuances of playing the corner spot.”

Now, it seems, Acker is still learning and still improving. Niners defensive coordinator Vic Fangio went into this training camp in need of playmakers in the secondary. Recently, Acker is trying to show he belongs.